DEBUGGER: Add "md5" command, to get the MD5 sum of entire files

This may make it easier to ask users for the MD5 sum of a file, in
case we suspect a bug report is caused by damaged files.
DEBUGGER: Add "md5mac" command to get MD5 sum of Mac resource fork.
DEBUGGER: Sort "md5" output, when using wildcards.
DEBUGGER: Changed usage output from "md5mac"

I don't know of any good way of transforming file names to base
file names, so document that "md5mac" expects the base file name.
Even though it currently will accept MacBinary file names.
DEBUGGER: Let "md5mac" print the MD5 sum of both resource and data
DEBUGGER: Add FIXME comment about file name vs base name
Merge pull request #497 from eriktorbjorn/md5-debug

Add "md5" command to the debugger